Thermally balanced hot runner nozzle

ABSTRACT

The present invention is directed to a nozzle for an injection molding machine. The nozzle includes a body defining a melt channel. A heater is connected to the nozzle body. A heat distributor is also connected to the nozzle body. The heat distributor is formed of a conductive material for distributing heat from the heater along the nozzle body.

FIELD OF THE INVENTION

[0001] This invention relates to molding machines and in particular tonozzles for molding machines.

BACKGROUND OF THE INVENTION

[0002] Molding machines include hot runner nozzles that define a meltchannel for passing molten material to a desired location such as a moldcavity. It is important that the molten material be kept at a desiredtemperature to ensure that it flows and cures properly. Typically, hotrunner nozzles are heated with a resistance heater that is wound aboutthe outer surface of the nozzle body. A thermocouple is disposed withinthe nozzle body to sense the body temperature and the resistance heateris operated by a control system to maintain the body at a desiredtemperature.

[0003] A problem with such conventional nozzles is that the temperaturewithin the nozzle varies over the length of the nozzle body. Usually,the ends of the nozzle tend to be much cooler than the middle portion ofthe nozzle due to heat loses occurring at the ends. As a result, it isdifficult to maintain the melt within the melt channel at a constantdesired temperature. This is problematic in particular for moltenmaterials that are sensitive to minor changes in temperature. If thetemperature is increased too much then the melt will burn in the middleportion of the nozzle, and if the temperature is decreased to avoidburning then the melt might have flow problems or other problems thatwill effect its ability to cure properly within the mold cavities.

[0004] There is a need for an apparatus to heat the melt channel withina nozzle body to a desired temperature that remains relatively constantover the length of the nozzle.

SUMMARY OF THE INVENTION

[0005] In one aspect the invention provides a nozzle for a moldingmachine comprising:

[0006] a nozzle body defining a melt channel;

[0007] a heater connected to said nozzle body along at least a portionof the length of said nozzle body; and

[0008] at least one heat distributor connected to said nozzle body, saidheat distributor being formed of a conductive material for distributingheat from said heater along said nozzle body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a better understanding of the present invention, and to showmore clearly how it may be carried into effect, reference will now bemade by way of example to the accompanying drawings. The drawings showpreferred embodiments of the present invention, in which:

[0010]FIG. 1 is a graph of nozzle temperature over the length of anozzle;

[0011]FIG. 2 is a sectional view of a nozzle in accordance with thepresent invention;

[0012]FIG. 3 is a transverse sectional view of the nozzle of FIG. 2taken along lines 3-3;

[0013]FIG. 4 is a sectional view of a second embodiment of nozzle inaccordance with the present invention;

[0014]FIG. 5 is a transverse sectional view of the nozzle of FIG. 4taken along lines 5-5;

[0015]FIG. 6 is a sectional view of a third embodiment of nozzle inaccordance with the present invention;

[0016]FIG. 7 is a transverse sectional view of the nozzle of FIG. 6taken along lines 7-7;

[0017]FIG. 8 is a transverse sectional view of the nozzle of FIG. 6taken along lines 8-8;

[0018]FIG. 9 is a transverse sectional view of the nozzle of FIG. 6taken along lines 9-9.

[0019]FIG. 10 is a sectional view of a fourth embodiment of nozzle inaccordance with the present invention;

[0020]FIG. 11 is a transverse sectional view of the nozzle of FIG. 10taken along lines 11-11;

[0021]FIG. 12 is a sectional view of a fifth embodiment of nozzle inaccordance with the present invention;

[0022]FIG. 13 is a transverse sectional view of the nozzle of FIG. 12taken along lines 13-13;

[0023]FIG. 14 is a transverse sectional view of a sixth embodiment ofnozzle in accordance with the present invention; and

[0024]FIG. 15 is a schematic view of an injection molding machine withnozzles in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] Referring to FIG. 1, a temperature profile over the length of aconventional hot runner nozzle is shown at 10. The profile 10 showslower temperatures 12 at the ends of the nozzle and higher temperatures14 at the middle of the nozzle. A desired temperature profile for anozzle in accordance with the present invention is shown at 16. Thedesired temperature is relatively constant over the length of thenozzle.

[0026] Referring to FIGS. 2 and 3, a nozzle in accordance with a firstembodiment of the present invention is shown generally at 20. The nozzle20 includes a body 22 that defines a melt channel 24. Nozzle body istypically formed of steel or other suitable materials known to personsskilled in the art. The nozzle has an inlet 26 defined at a first end 28and an outlet 30 defined at a second end 32. Second end 32 typically isdefined as a frustoconical tip. A collar 34 is defined at the first endfor mounting the nozzle 20 to a manifold 36.

[0027] Nozzle 20 includes a continuous channel 40 defined in its outersurface for receiving a resistance heater, such as for example a coilheater 42. Examples of suitable resistance heaters are disclosed in U.S.Pat. Nos. 4,557,685, 5,266,023 and 5,704,113 which are all herebyincorporated by reference. Resistance coil heater 42 is wound over thelength of the nozzle and is preferably disposed fully within channel 40such that the outer surface of the heater 42 lies generally flush withthe outer surface of the nozzle body 22. Heater 42 may be secured tochannel 40 with a press friction fit or through metalurgical bondingsuch as brazing or other securing means known to persons skilled in theart. A thermocouple 44 is disposed in nozzle body 22 for sensing thetemperature of the nozzle body 22 adjacent to melt channel 24. Heater 42is coupled to a power supply 46 for powering the heater 42. Thethermocouple 44 and heater 42 are connected to a control system (notshown) that monitors the temperature of nozzle body 22 and operatesheater 42 as required to maintain desired temperature profile 16. Amanifold heater 48 is disposed in manifold 36 to similarly heat moltenmaterial passing through a manifold melt channel 52.

[0028] A heat distributor 60 is disposed on nozzle body 22 over adesired portion of its length. Heat distributor 60 is formed of aconductive material such as copper or a copper alloy that will conductheat produced by heater 42 along the length of heat distributor 60. Heatdistributor 60 may be preformed as a hollow sleeve that is closelyfitted to nozzle body by means of a friction fit or by means ofbraising, welding, or other attachment methods known to those skilled inthe art. Alternatively, heat distributor 60 may be applied to the outersurface of nozzle body 22 by spraying or dipping the conductive materialdirectly onto nozzle body 22. Preferably, heat distributor 60 is indirect physical contact with heater 42 and with nozzle body 22 in orderthat an optimum heat transfer and distribution can be achieved. As aresult, heat distributor 60 acts to distribute heat sufficiently overits length to produce a relatively constant temperature profile 16 overthe corresponding length of nozzle 20.

[0029] Referring to FIGS. 4 and 5, a second embodiment of nozzle 20 inaccordance with the present invention is shown. For convenience,corresponding elements as described above are assigned correspondingreference numbers.

[0030] In the second embodiment of nozzle 20, nozzle body 22 has heatdistributor 60 disposed upon its outer surface. A hollow heater sleeve70 is then disposed on the outer surface of heat distributor 60. Heatersleeve 70 defines continuous channel 40 for receiving heater 42. Heater42 is connected to power supply 46 for powering the heater 42. A secondheat distributor 60′ is disposed externally of heater sleeve 70 tofurther aid in distributing heat along the desired length of nozzle body22. A thermal insulator 72 such as a ceramic or other suitableinsulation material known to those skilled in the art may in someinstances be disposed externally to heat distributor 60′.

[0031] Referring to FIGS. 6-9, a third embodiment of nozzle inaccordance with the present invention is shown. Again, for convenience,corresponding elements to the embodiments described above are givencorresponding reference numbers.

[0032] The third embodiment of nozzle 20 includes nozzle body 22 whichdefines in its outer surface continuous channel 40 for receiving heater42. Nozzle body 22 is configured to include a reduced diameter portion80 at an intermediate region between the first and second ends 26, 32 ofnozzle 20. Reduced diameter portion 80 provides a region of heat loss toreduce the likelihood of high temperature 14 in the intermediate regionof nozzle 20. Reduced diameter portion 80 provides a smaller mass totransfer less heat from the heater 42 to the molten material flowingthrough the melt channel.

[0033] Heater 42 is also disposed at second end 0.32 of nozzle body 22for maintaining temperature of the melt within nozzle body 22 prior toexiting from outlet 30.

[0034] Heat distributor 60 is disposed on nozzle body 22 fordistributing heat along the length of nozzle body 22 to achieverelatively constant temperature profile 16. Heat distributor 60 includesapertures 82 overlying reduced diameter portions 80 of nozzle body 22 toallow heat loss over the intermediate region of nozzle body 22. Heatdistributor 60 also is disposed at second end 32 of nozzle body 22 todistribute heat over the length of second end 32. The location of heatdistributor 60 on second end 32 is of particular utility when second end32 is formed as by frustoconical tip where it is difficult to disposeheater 42 adjacent to outlet 30.

[0035] Referring to FIGS. 10-11, a fourth embodiment of nozzle inaccordance with the present invention is shown. Again, for convenience,corresponding elements to the embodiments described above are givencorresponding reference numbers.

[0036] The fourth embodiment of nozzle 20 includes nozzle body 22 withmelt channel 24. Heater 42 is a film heater such as is disclosed in thefollowing patents which are hereby incorporated by reference: EP963829,EP312029, WO0023245, and WO0117317. Surrounding film heater 42 is anelectrical insulator 90 that protects the film heater 42. Heatdistributor 60 is then disposed over electrical insulator 90.

[0037] Referring to FIGS. 12-13, a fifth embodiment of nozzle inaccordance with the present invention is shown. For convenience,corresponding elements to the embodiments described above are givencorresponding references numbers.

[0038] The fifth embodiment of nozzle 20 includes nozzle body 22 thatdefines melt channel 24. Nozzle heater 42 is in the form of a resistancewire that is disposed in a dielectric material disposed around nozzlebody 22. Nozzle heater 42 includes a first dielectric layer 92 that isdisposed over nozzle body 22. A resistive wire 94 is then wrapped aroundnozzle body 22 over first dielectric layer 92. A second dielectric layer96 is then disposed over resistive wire 94 and first dielectric layer92. This type of heater 42 is described in more detail in PCTapplication PCT/CA01/00274 which is hereby incorporated by reference.Heat distributor 60 is disposed over second dielectric layer 96 in orderto distribute heat from resistance wire heater 42 over the length ofheat distributor 60.

[0039] Referring to FIG. 14, a sixth embodiment of nozzle 20 inaccordance with the present invention is shown. Again, for convenience,corresponding elements to the embodiments described above are givencorresponding reference numbers.

[0040] The sixth embodiment of nozzle 20 is similar to the firstembodiment described above. Nozzle 20 includes nozzle body 22 whichdefines in its outer surface continuous channel 40 for receiving heater42. Heat distributor 60 is disposed on nozzle body 22 over a desiredportion of its length. Heat distributor 60 includes a longitudinal slit98 to accommodate thermocouple 44 so that the thermocouple 44 may bedisposed against nozzle body 22.

[0041] Referring to FIG. 15, a schematic view of an injection moldingmachine 100 is shown with nozzles 20 in accordance with the presentinvention. For convenience, corresponding elements to the embodimentsdescribed above are given corresponding reference numbers.

[0042] The injection molding machine 100 includes an inlet nozzle 102that is connected to manifold 36. Manifold 36 includes melt channel 104for distributing melt from inlet nozzle 102 to injection nozzles 20.Injection nozzles 20 include collar 34 for mounting injection nozzles 20to manifold 36. Injection nozzles 20 are connected to mold cavity 106 inknown manner for introducing the molten material into mold cavity 106.Injection nozzle 20 include nozzle body 22 that is heated with heater42. Heat distributor 60 is disposed over nozzle body 22 for distributingheat from heater 42 over the length of heat distributor 60. Heatdistributor 60 thus acts to distribute heat sufficiently over its lengthto produce a relatively constant temperature profile 16 over thecorresponding length of nozzle 20.

[0043] It is to be understood that what has been described is apreferred embodiment to the invention. If the invention nonetheless issusceptible to certain changes and alternative embodiments fullycomprehended by the spirit of the invention as described above, and thescope of the claims set out below.

We claim:
 1. A nozzle for a molding machine comprising: a nozzle bodydefining a melt channel; a heater connected to said nozzle body along atleast a portion of the length of said nozzle body; and at least one heatdistributor connected to said nozzle body, said heat distributor beingformed of a conductive material for distributing heat from said heateralong said nozzle body.
 2. A nozzle as claimed in claim 1 furthercomprising a continuous channel defined in said nozzle body forreceiving said heater.
 3. A nozzle as claimed in 2 wherein said heateris disposed in said continuous channel such that said heater isgenerally flush with an outer surface of said nozzle body.
 4. A nozzleas claimed in claim 2 wherein said heater is pressed in said continuouschannel.
 5. A nozzle as claimed in claim 2 wherein said heater is brazedin said continuous channel.
 6. A nozzle as claimed in claim 1 whereinsaid heat distributor is a preformed hollow sleeve.
 7. A nozzle asclaimed in claim 1 where said heat distributor is fluidly deposited onsaid nozzle body.
 8. A nozzle as claimed in claim 1 further comprising athermal insulator disposed over at least a portion of said heatdistributor.
 9. A nozzle as claimed in claim 1 wherein said heatdistributor is brazed to said nozzle body.
 10. A nozzle as claimed inclaim 1 wherein said heater is a film heater.
 11. A nozzle as claimed inclaim 1 wherein said heater is a resistance wire heater disposed in adielectric material.
 12. A nozzle as claimed in claim 1 wherein saidheater is metallurgically bonded to said nozzle body.
 13. A nozzle asclaimed in claim 6 wherein said sleeve defines a longitudinal slit forpositioning a thermocouple proximate to said nozzle body.
 14. Aninjection molding machine comprising: an inlet nozzle for introducing amolten material to the molding machine: a manifold in communication withsaid inlet nozzle for receiving and distributing said molten material; aplurality of injection nozzles in communication with said manifold forreceiving said molten material, said injection nozzles being incommunication with corresponding mold cavities, each said injectionnozzle having a heater connected to a nozzle body along at least aportion of the length of the nozzle body and at least one heatdistributor connected to the nozzle body for distributing heat from saidheater along said nozzle body.
 15. A nozzle as claimed in claim 14further comprising a continuous channel defined in said nozzle body forreceiving said heater.
 16. A nozzle as claimed in 15 wherein said heateris disposed in said continuous channel such that said heater isgenerally flush with an outer surface of said nozzle body.
 17. A nozzleas claimed in claim 15 wherein said heater is pressed in said continuouschannel.
 18. A nozzle as claimed in claim 15 wherein said heater isbrazed in said continuous channel.
 19. A nozzle as claimed in claim 14wherein said heat distributor is a preformed hollow sleeve.
 20. A nozzleas claimed in claim 14 where said heat distributor is fluidly depositedon said nozzle body.
 21. A nozzle as claimed in claim 14 furthercomprising a thermal insulator disposed over at least a portion of saidheat distributor.
 22. A nozzle as claimed in claim 14 wherein said heatdistributor is brazed to said nozzle body.
 23. A nozzle as claimed inclaim 14 wherein said heater is a film heater.
 24. A nozzle as claimedin claim 14 wherein said heater is a resistance wire heater disposed ina dielectric material.
 25. A nozzle as claimed in claim 14 wherein saidheater is metallurgically bonded to said nozzle body.
 26. A nozzle asclaimed in claim 19 wherein said sleeve defines a longitudinal slit forpositioning a thermocouple proximate to said nozzle body.